| 1. |
- Berglund, Martin, 1985-
(författare)
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Miniature Plasma Sources for High-Precision Molecular Spectroscopy in Planetary Exploration
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The prospect of finding life outside Earth has fascinated mankind for ages, and new technology continuously pushes the boundary of how remote and how obscure evidence we can find. Employing smaller, or completely new, types of landers and robots, and equipping them with miniature instruments would indeed revolutionize exploration of other planets and moons.In this thesis, microsystems technology is used to create a miniature high-precision isotope-resolving molecular spectrometer utilizing the optogalvanic effect. The heart of the instrument, as well as this thesis, is a microplasma source.The plasma source is a split-ring resonator, chosen for its simplicity, pressure range and easily accessible plasma, and modified to fit the challenging application, e.g., by the adding of an additional ground plane for improved electromagnetic shielding, and the integration of microscopic plasma probes to extract the pristine optogalvanic signal.Plasma sources of this kind have been manufactured in both printed circuit board and alumina, the latter for its chemical inertness and for compatibility with other devices in a total analysis system. From previous studies, classical optogalvanic spectroscopy (OGS), although being very sensitive, is known to suffer from stability and reproducibility issues. In this thesis several studies were conducted to investigate and improve these shortcomings, and to improve the signal-to-noise ratio. Moreover, extensive work was put into understanding the underlying physics of the technique.The plasma sources developed here, are the first ever miniature devices to be used in OGS, and exhibits several benefits compared to traditional solutions. Furthermore, it has been confirmed that OGS scales well with miniaturization. For example, the signal strength does not decrease as the volume is reduced like in regular absorption spectroscopy. Moreover, the stability and reproducibility are greatly increased, in some cases as much as by two orders of magnitude, compared with recent studies made on a classical OGS setup. The signal-to-noise ratio has also been greatly improved, e.g., by enclosing the sample cell and by biasing the plasma. Another benefit of a miniature sample cell is the miniscule amount of sample it requires, which can be important in many applications where only small amounts of sample are available.To conclude: With this work, an important step toward a miniature, yet highly performing, instrument for detection of extraterrestrial life, has been taken.
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| 2. |
- De Geer, Jakob, 1970-
(författare)
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On the use of computed tomography in cardiac imaging
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BackgroundCardiac Computed Tomography Angiography (CCTA) is becoming increasingly useful in the work‐up of coronary artery disease (CAD). Several potential methods for increasing the diagnostic yield of cardiac CT are available.Purpose Study I: To investigate whether the use of a 2‐D, non‐linear adaptive noise reduction filter can improve CCTA image quality.Study II: To evaluate the variation in adenosine stress dynamic CT perfusion (CTP) blood flow as compared to stress 99mTc SPECT. Secondly, to compare the perfusion results from manual and automatic myocardial CTP segmentation.Study III: To evaluate the accuracy of non‐invasive, CCTA‐derived Fractional Flow Reserve (cFFR).Study IV: To evaluate the prognostic value of CCTA in terms of major adverse cardiac events (MACE).Materials and methodsStudy I: Single images from 36 consecutive CCTA exams performed with two different dose levels were used. Image quality in full dose, low‐dose and noise‐reduced low‐dose images was graded using visual grading analysis. Image noise was measured.Study II: CTP and SPECT were performed in 17 patients, and the variation in per AHA‐segment blood flow was evaluated and compared. CTP results from manual and automated image segmentation were compared.Study III: CCTA datasets from 21 patients were processed using cFFR software and the results compared to the corresponding invasively measured FFR (invFFR).Study IV: 1205 consecutive patients with chest pain of unknown origin underwent CCTA. Baseline data and data on subsequent MACE were retrieved from relevant registries. Survival, hazard ratios and the three‐year incidence of cardiac events and readmissions were calculated.Results Study I: There was significant improvement in perceived image quality for all criteria when the filter was applied, and a significant decrease in image noise.Study II: The correlation coefficients for CTP vs. SPECT were 0.38 and 0.41 (p<0.001, for manual and automated segmentation respectively. Mean per patient CTP blood flow in normal segments varied between 94‐183 ml/100 ml tissue/min for manual segmentation, and 104‐196 ml/100 ml tissue/min for automated segmentation. The Spearman rank correlation coefficient for manual vs. automated segmentation CTP was ρ = 0.88 (p<0.001) and the Intraclass Correlation Coefficient (ICC) was 0.93 (p<0.001).Study III: The Spearman rank correlation coefficient for cFFR vs. invFFR was ρ = 0.77 (p<0.001) and the ICC was 0.73 (p<0.001). Sensitivity, specificity, positive predictive value and negative predictive value for significant stenosis (FFR<0.80, per vessel) were 0.83, 0.76, 0.56 and 0.93 respectively.Study IV: The hazard ratio for non‐obstructive CAD vs. normal coronary arteries was 5.13 (95% C.I 1.03‐25.43, p<0.05), and 151.40 (95% C.I 37.03‐619.08, p<0.001) for obstructive CAD vs. normal coronary arteries. The three‐year incidence of MACE was 1.1% for patients with normal vessels on CCTA, 2.5% for patients with non‐obstructive CAD and 42.7% for patients with obstructive CAD (p<0.001).Conclusions:Study I: Image quality and noise levels of low dose images were significantly improved with the filter, even though the improvement was small compared to the image quality of the corresponding diastolic full‐dose images.Study II: Correlation between dynamic CTP and SPECT was positive but weak. There were large variations in CTP blood flow in normal segments on SPECT, rendering the definition of an absolute cut‐off value for normal vs. ischemic myocardium difficult. Manual and automatic segmentation were equally useful.Study III: The correlation between cFFR and invFFR was good, indicating that noninvasively estimated cFFR performs on a similar level as invasively measure FFR. Study IV: The long‐term risk for MACE was very low in patients without obstructive CAD on CCTA, though there seemed to be a substantial increase in the risk for MACE even in patients with non‐obstructive CAD as compared to normal coronary arteries. In addition, even patients with normal coronary arteries or non‐obstructive CAD continued to have a substantial number of readmissions for chest pain or angina pectoris.
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| 3. |
- Eek-Karlsson, Liselotte, 1955-
(författare)
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Ungas samspel i sociala medier : Att balansera mellan ansvar och positionering
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The growing communication that takes place between young people today causes concern. The purpose of this study is to develop in – depth knowledge of the interaction that young people engage in online. The pedagogic interest is based on an investigation of conditions for social learning and social integration that exist in practice, which unfolds in virtual spaces created by social media. The technology referred to in this thesis is considered to be a social construction, which entails that values circulate between people, technology, and society. The theoretical point of departure is based on a pedagogic theory, which proposes that people develop their ability to cooperate, their social identity, and their understanding of the world through interaction with others. This dissertation includes three studies. The first study investigates support and harassment online (for example, insults). The second study is conducted for the purpose of revealing the discursive patterns in young people’s argumentation, based on a series of interviews. Finally, a text analysis of Facebook’s policy document was performed, with focus on the democratic values that are mediated via this document. The overall result is that considerably more young people feel that they are supported in social media, than those who are harassed. Both a supportive culture and a harassing culture can be defined however. The more often young people support their friends, the more often they find themselves to be the recipient of support. The same relationship pertains for harassing communication. Reciprocity, respect, and being responsible are dominant themes in a close circle of friends. In interaction with friends who are not members of the close circle of friends, communication is characterised by asymmetry and control. The imposition of discipline takes place as a function of both gender and status. The risk of being subject to reprisals is great, if the prevailing system of norms is violated. Young people’s social interaction in virtual spaces tends to be dominated by marketization where strategic behaviour, which primarily is a function of the individual’s social position and profit interest, is observed.
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| 4. |
- Kataria, Bharti, 1955-
(författare)
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Visual grading evaluation of reconstruction methods and dose optimisation in abdominal Computed Tomography
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since its introduction in the 1970’s CT has emerged as a modality of choice because of its high sensitivity in producing accurate diagnostic images. A third of all Computed Tomography (CT) examinations are abdominal CTs which deliver one of the highest doses among common examinations. An increase in the number of CT examinations has raised concerns about the negative effects of ionising radiation as the dose is cumulative over the life span of the individual. Image quality in CT is closely related to the radiation dose, so that a certain dose with an associated small, but not negligible, risk is a prerequisite for high image quality. Typically, dose reduction in CT results in higher noise and a decrease in low contrast resolution which can be detrimental to the image quality produced. New technology presents a wide range of dose reduction strategies, the latest being iterative reconstruction (IR).The aim of this thesis was to evaluate two different classes of iterative reconstruction algorithms: statistical (SAFIRE) and model-based (ADMIRE) as well as to explore the diagnostic value of a low-dose abdominal CT for optimisation purposes.This thesis included a total of 140 human subjects in four image quality evaluation studies, three of which were prospective studies (Papers I, II and IV) and one retrospective study (Paper III). Visual grading experiments to determine the potential dose reductions, were performed with pairwise comparison of image quality in the same patient at different tube loads (dose) and reconstructed with Filtered back projection (FBP) and SAFIRE strength 1 in a low-dose abdominal CT (Paper I) and FBP and ADMIRE strengths 3 and 5 in a standard dose abdominal CT (Paper II). Paper IV evaluated the impact of slice thicknesses in CT images reconstructed with ADMIRE strengths 3 and 5 when comparing multiplanar reconstruction (MPR) formatted images in a standard dose abdominal CT. Paper III, on the other hand, was an absolute assessment of image quality and pathology between the three phases of a CT Urography (CTU) protocol to explore the diagnostic value of low-dose abdominal CT. The anonymised images were displayed in random order and image quality was assessed by a group of radiologists using image quality criteria from the “European guidelines of quality criteria for CT”. The responses from the reviewer assessment were analysed statistically with ordinal logistic regression i.e. Visual Grading Regression (VGR).Results in Paper I show that a small dose reduction (5-9 %) was possible using SAFIRE strength 1and indicated the need for further research to evaluate the dose reduction potential of higher strengths of the algorithm. In Paper II a 30% dose reduction was possible without change in ADMIRE algorithm strength as no improvement in image quality was observed between tube loads 98- and 140 mAs. When comparing tube loads 42 and 98 mAs, further dose reduction was possible with ADMIRE strength 3 (22-47%). However, for images reconstructed with ADMIRE strength 5, a dose reduction of 34-74% was possible for some, but not all image criteria. Image quality in low-contrast objects such as the liver parenchyma, was affected and a decline in diagnostic confidence was observed. Paper IV showed potential dose reductions are possible with increasing slice thickness from 1 mm to 2 mm (24-35%) and 1 mm to 3mm (25-41%). ADMIRE strength 3 continued to provide diagnostically acceptable images with possible dose reductions for all image criteria assessed. Despite objective evaluations showing a decrease in noise and an increase in contrast to noise ratio, ADMIRE strength 5 had diverse effects on the five image criteria, depending on slice thickness and further dose reductions were limited to certain image criteria. The findings do not support a general recommendation to replace ADMIRE3 with ADMIRE5 in clinical abdominal CT protocols.Paper III studied another aspect of optimisation and results show that visualisation of renal anatomy was as expected in favour of the post-contrast phases when compared to the native phase. Assessment of pathology showed no significant differences between the three phases. Significantly higher diagnostic certainty for renal anatomy was observed for the post-contrast phases when compared to the native phase. Significantly high certainty scores were also seen for the nephrographic phase for incidental findings. The conclusion is that a low-dose series seems to be sufficient as a first-line modality in certain patient groups.This thesis clinically evaluated the effect of IR in abdominal CT imaging and estimated potential dose reductions. The important conclusion from papers I, II and IV is that IR improves image quality in abdominal CT allowing for some dose reductions. However, the clinical utility of the highest strength of the algorithm is limited to certain criteria. The results can be used to optimise the clinical abdominal CT protocol. The conclusion from paper III may increase clinical awareness of the value of the low-dose abdominal protocol when choosing an imaging method for certain patient groups who are more sensitive to radiation.
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| 5. |
- Kihlberg, Johan, 1970-
(författare)
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Magnetic Resonance Imaging of Myocardial Deformation and Scarring in Coronary Artery Disease.
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although improved treatments have reduced the rates of acute complications from myocardial infarction, sequelae such as heart failure and sudden death threaten the future wellbeing of those patients. Secondary prevention after myocardial infarction is related to cardiovascular risk factors and the effect of the infarct on left ventricular function. Cardiovascular magnetic resonance imaging (CMR) is necessary to determine the size of the infarct scar and can with great precision determine left ventricular volumes, left ventricular ejection fraction, and deformation (strain and torsion). The purpose of this thesis was to improve on CMR methods to facilitate image acquisition and post processing in patients with high risk of coronary artery disease (CAD).In Paper 1, a three-dimensional phase-sensitive inversion-recovery (3D PSIR) sequence was modified to measure T1 during a single breath hold. The measured T1 values were used to extrapolate a map of T1 relaxation, which avoided the time-consuming manual determination of the inversion time. The data collection consisted of phantom experiments, Monte Carlo simulations of the effect of various heart rates, and clinical investigation of 18 patients with myocardial infarction. Scar images created with the modified sequence were compared to those created with the standard sequence. The 3D PSIR sequence was able to measure T1 relaxation with a high accuracy up to 800 ms, which is in the suitable range for scar imaging. Simulated arrhythmias showed that the method was robust and able to tolerate some variation in heart rate. The modified sequence provides measurements of inversion time that can be used to facilitate standard scar imaging or to reconstruct synthetic scar images. Images of infarct scar obtained with the 3D PSIR sequence bore striking similarity to images obtained with the standard sequence.In Paper 2, 125 patients with high risk of CAD were investigated using the displacement encoding with stimulated echoes (DENSE) sequence. Image segments with infarct scar area >50% (transmurality) could be identified with a sensitivity of 95% and a specificity of 80% based on circumferential strain calculated from the DENSE measurements. The DENSE sequence was also applied in other directions, but its sensitivity and specificity to detect scar was lower than when used for circumferential strain.In Paper 3, 90 patients with high risk of CAD were examined by DENSE, tagging with harmonic phase (HARP) imaging and cine imaging with feature tracking (FT), to detect cardiac abnormalities as manifested in end-systolic circumferential strain. Circumferential strain calculated with DENSE had higher sensitivity and specificity than the competing methods to detect infarction with transmurality >50%. Global circumferential strain measured by DENSE correlated better with global parameters such as left ventricular ejection fraction, myocardial wall mass, left ventricular end-diastolic and end-systolic volume; than strain measured by FT or HARP.In Paper 4, myocardial torsion was investigated using DENSE, HARP, and FT in 48 patients with high risk of CAD. Torsion measured by each of the three methods was correlated with other global measures such as left ventricular ejection fraction, left ventricular mass, and left ventricular end-diastolic and end-systolic volumes. The torsion measurements obtained with DENSE had a stronger relationship with left ventricular ejection fraction, left ventricular mass, and volumes than those obtained with HARP or FT.DENSE was superior to the other methods for strain and torsion measurement and can be used to describe myocardial deformation quantitatively and objectively.
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| 6. |
- Kälvesten, Johan, 1980-
(författare)
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Automatic image analysis for decision support in rheumatoid arthritis and osteoporosis
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low-energy trauma and fragility fractures represent a major public health problem. The societal cost of the fragility fractures that occurred in Sweden 2010 has been estimated at €4 billion.In rheumatoid arthritis (RA), patient outcomes have improved greatly in recent years. However, the therapeutic decision making is still hampered by a lack of effective validated biomarkers. The cost of RA in Sweden 2010 has been estimated at €600 million, of which biologic drugs was €180 million.Digital X-ray radiogrammetry (DXR) is a method to measure bone mineral density (BMD) in the metacarpals of the hand. It can be applied opportunistically in several workflows where a person is already at an X-ray machine, including fracture repositioning follow up, mammography screening and hand imaging in RA. This thesis explored DXR-BMD as a marker to identify individuals who would benefit from anti-osteoporotic treatment, change rate of DXR-BMD as a biomarker in RA and under what conditions historical X-ray images can be used to estimate DXR-BMD. An automated method for measurement of joint space width in metacarpophalangeal and interphalangeal joints was also developed and evaluated as a biomarker in RA.Low DXR-BMD was predictive for hip fractures and predicted fragility fractures to a comparable degree as other BMD measurement sites. Rapid decrease of DXR-BMD was a strong and independent predictor for progression of radiographic damage in RA when manual radiographic progression scores were not available. Change of metacarpal joint space width was a statistically significant but weak predictor of joint space narrowing score progression. Guidelines and considerations for use of historical X-ray radiographs for DXR-BMD measurements in clinical trials have been developed and published.
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| 7. |
- Lekholm, Ville, 1976-
(författare)
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High-Temperature Microfluidics for Space Propulsion
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, microfabrication methods and tools for analysis of heated cold-gas microthrusters are presented, with the aim of improving their reliability and performance. Cold-gas thrusters operate by accelerating pressurized gas through a nozzle. These thruster systems are very straightforward in both design and operation, relying on little more than a pressurized tank, a valve, and a nozzle. This makes them suitable for miniaturization, enabling their use on very small spacecraft. However, an inherent drawback with cold-gas thrusters is their low propellant efficiency – in thrusters known as specific impulse, or Isp. This is compounded by the fact that when reducing length, the volume, e.g., that of the propellant tank, reduces with the cube of the length, meaning that the maximum amount of storable fuel reduces quickly. Hence, maximizing fuel efficiency is even more important in miniaturized systems. Still, because of their other advantages, they remain suitable for many missions. Schlieren imaging – a method of visualizing differences in refractive index – was used thrughout this thesis to visualize exhaust jets from microthrusters, and to find leaks in the components. It was found that effects of the processing of conventionally fabricated silicon nozzles, resulted in a misalignment of up to 3° from the intended thrust vector, increasing propellant consumption by up to 5%, and potentially causing unintended off-axis acceleration of the spacecraft. Schlieren imaging was also used to verify that the exhaust from thrusters fabricated with close to circular cross-sections was well behaved. These nozzles did not suffer from the previous misalignment issue, and the shape of the cross-section decreased viscous losses. For applications requiring higher temperatures, a microthruster nozzle with an integrated flow sensor was fabricated from tape cast yttria stabilized zirconia. The ceramic substrate enabled heater temperatures of the nozzle exceeding 1000 °C, resulting in an increase in Isp of 7.5%. Integration of a flow sensor allowed the elimination of couplings and reduced the number of interfaces, thereby reducing the overall risk of failure. Close integration of the sensor allowed moving the point of measurement closer to the nozzle, enabling improved reliability of the measurements of the propellant consumption. The temperature of the heater, in combination with the ion conductive properties of the substrate proved to be a limiting factor in this design. Two routes were explored to overcome these problems. One was to use the temperature dependence of the ion conductivity as a sensing principle, thereby demonstrating a completely new flow sensor principle, which results in better calibration, tighter integration, and 9 orders of magnitude stronger signal. The other was using hafnium oxide, or hafnia, as a structural material for high-temperature micro-electromechanical systems. This involved developing a recipe for casting hafnia ceramic powder, and determining the Young's modulus and thermal shock resistance of the cast samples, as well as studying the minimum feature size and maximum aspect ratio of cast microstructures.
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| 8. |
- Persson, Anders, 1974-
(författare)
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Lärartillvaro och historieundervisning : innebörder av ett nytt uppdrag i de mätbara resultatens tid
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Swedish compulsory school has recently been subjected to a number of political reforms. Between 2011 and 2014, for example, earlier grades, more national tests and a new curriculum plan (Lgr 11) were to be implemented. This thesis aims to examine those changes as they were experienced by teachers who teach history in Swedish upper primary schools. The theoretical framework is in-spired by existential philosophy, primarily as formulated in the works of Martin Heidegger and Hanna Arendt. In this way, the study highlights the teachers’ lived experience by making use of the concepts yearning, appearance, acting and mood.The study comprises of 36 interviews with 26 informants. The interviews were carried out and transcribed during 2014. The questions focus on both the existential being of the teachers’ lives as well as the ideological function of the history subject. This highly renders in the issue of how lived experiences of a specific school reform corresponded to the teachers’ own perception of a mean-ingful history education. Both the yearnings that were expressed by the participants and their de-scriptions of what they have experienced, have been related to the overall educational ideological functions stated by Gert Biesta (socialisation, subjectification and qualification) and Jonas Aspelin (existentialisation).Although the teachers’ narratives were greatly varied in some aspects, their interpretations of the new assignment seemed to be quite homogenous. Most of the teachers portrayed a situation characterised by performativity. Measurable knowledge and more frequent documentation seemed to be prioritised. Some of them stressed that they experienced less autonomy. In terms of history, the new curriculum was associated with more content knowledge, cognitive skills and procedural abilities. From the teachers’ perspective, pure qualification, rather than subjectification and social-isation, characterised the new curriculum.Still, the teachers’ feelings towards the curricular changes showed a great deal of divergence. Some of them embraced most of the new aspects. They claimed that clearly formulated require-ments in the history curricula provided them with security. They declared that their history teaching to some extent became more professional. In line with such beliefs, some teachers asserted that the strengthened focus on analytical skills improved their teaching. Particularly those who ex-pressed that they preferred such analytic procedural approaches described their experience in terms of confirmation and approval. Others appeared to struggle with the changes. While a few teachers even tried to resist the curricular changes, some found themselves forced to endure what appeared to be a totally new situation. They expressed disbelief, frustration and pain. Notably it was those most devoted to the existentialisational function of history teaching that usually seemed to express such alienation. As argued, they appeared to long for a lost possibility to engage their pupils, to bring history alive and to make meaning of the past.
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